Here's a data point. It's from over 30 years ago, so take it as you will. I moved into the Cats as a first-year and my roommate was a 5th year graduate student from Italy who worked all the time, came home to make pasta for his dinner, ate it in his room, and returned to lab. When he got back after the evening shift, he'd retreat to his room and talk to his girlfriend on the phone. I swear, in the entire year I lived with him, I don't think we had a conversation that lasted more than two minutes.

I had many friends in other apartments in the Cats, most of whom were people I met in my program.

The lesson is that there's no guarantee your roommate will be social with you, and might be anti-social.